1. Field of the Invention
The invention relates to the manufacture of yarn packages for yarns such as glass yarns, and more particularly to the manufacture of frustoconical packages.
2. Description of Related Art
Yarn packages in the form of bobbins are a standard means of temporarily storing yarn, in order subsequently for it to be fed into yarn-handling machines, for example textile machines.
In the case of glass yarns, glass filaments obtained by molten glass flowing through orifices in a bushing are drawn. Next, these filaments are coated with a sizing composition by a coater so as to facilitate the fiberizing and the collecting of the filaments into a yarn and to increase their mechanical properties, especially upon ageing. These filaments are then brought together into a combining device in order to create the yarn to be wound. The yarn coming from the combining device is wound around a support which lies in a horizontal plane perpendicular to the vertical plane in which the yarn arrives and is driven in a rotational movement at a constant speed. Usually, the yarn to be wound runs over the surface of a yarn guide which is located between the combining device and the support and moves in a backward and forward motion parallel to the longitudinal axis of the rotating support.
The bobbin of yarn thus obtained is called a cake. However, a cake is rarely used directly for feeding the yarn into textile machines for example.
This is because textile machines operate at high speed and the yarn must then be easily extractable from the bobbin to avoid any rubbing which could cause a break, something which is difficult to achieve using cakes. It is then necessary to manufacture, from these intermediate bobbins called cakes, cyclindrical bobbins from the yarn of which is twisted.
However, to avoid these various steps, namely cake manufacture followed by unwinding, in order to rewind yarn that has previously undergone a twist, which steps are long and require numerous means, frustoconical bobbins have been formed without manufacturing an intermediate cake, the yarn of which comes directly from the bushing and is not twisted.
This is because frustoconical shapes prevent the yarn from twisting and facilitate high-speed unwinding, the yarn being driven along the axis of the bobbin towards its smallest diameter and consequently moving immediately away from the bobbin as soon as a coil becomes detached therefrom.
Application FR 2,703,671 teaches a method of winding yarn for the formation of a frustoconical bobbin using a drawn yarn that has come directly from a bushing and has not undergone a twisting operation. The yarn, which is taken through the yarn guide, is wound around a support fastened at its base to a flange and placed vertically, the yarn guide moving in a backward and forward motion parallel to the longitudinal axis of the support. To produce the frustoconical shape of the bobbin, the solution proposed is to use a drawing device, placed after the device for combining the filaments and a dancer roll placed between the drawing device and the yarn guide. The dancer roll can rotate freely about its spindle, which is fastened to the end of a spring-loaded arm, thereby making it possible to impose a predetermined tension in the yarn to be wound.
The frustoconical shape of the bobbin, the base of which consists of the flange, is then obtained by giving the speed of rotation of the drawing device a constant value and by slaving the speed of movement of the yarn guide and the speed of rotation of the support.
However, such a solution requires a novel structure of the implementation device by, on the one hand, winding the yarn onto a support placed vertically and, on the other hand, using a drawing device and a dancer roll. The existing structures therefore have to undergo significant technical modifications, requiring some financial investment which is not negligible in a manufacturing plant.
Furthermore, the addition of a flange to the base of the support is not without problems as regards precision in depositing the yarn in this region. Thus, the yarn at the flange may either be laid down in an excess amount, which, when unwinding it, results in take-up as a packet, causing the yarn then to break, or be laid down in an insufficient amount, which then causes fraying of the yarn when unwinding it, caused by it being pinched between various layers of coils.
Finally, for bobbins of this type, the yarn of which has not undergone a twisting operation and is not wavy, it is common to encounter yarn damage problems since the crossover of the non-twisted yarn, that is to say the angle between two intersecting coils, is not large enough. This is because when this angle is too small, should a filament of the yarn be pinched between two coils of the bobbin, the continuity of the unwinding operation will result in the loss of one or more filaments from the yarn at the pinching point, resulting in the deterioration of the yarn and the formation of a ring by filament accumulation.